Bridge over Middle Peak Quarry 1920

The bridge in the picture has been blown up, but in earlier days it was
very important to local people living near the top of Green hill. It
enabled them to move heavy loads up to and from Rise End, which otherwise
could not be taken up the road from Wirksworth. Known as the Monkey Hole,
the bridge appears to have got its name following the boast of the owner
of a monkey, that the animal could retrieve a coin from anywhere. A local
man took up the challenge and threw the coin over the bridge for the monkey
to retrieve.

from "Meccano Magazine" July 1957, page 318

Inside the Monkey Hole

The Monkey Hole is deep and dark. It
got its name from a story of days gone
by of an Italian organ grinder who used to
entertain men working in the quarry, for
that is what the Monkey Hole once was.
From its top the organ grinder dangled a
rope on which his monkey would perform
tricks. One day the rope broke and the
monkey was killed. This ended the
performances, but the name has stuck
ever since.

This remarkable quarry is in the limestone
district near Wirksworth in Derbyshire,
and it is as remarkable for its shape as
for its name. From the pictures on these pages
you can see that its
sides are almost vertical, and that it can
only be entered through a narrow cleft in
the rocks. On entering it through the cleft
it is found to have a floor about 100 ft long
and 50 ft wide, and its sided tower up to a
height of about 150 ft. The floor is now
clear and level, but many thousand tons of
debris have been removed from it, and it is
actually, 10 ft lower than when the
quarrymen abandoned it.

The Monkey Hole was cleared in
this way because an entirely new use
has been found for it - the testing of
tall structures such as masts and
towers. These must be able to resist
the pressure of the wind, which of
course can vary from a gentle zephyr
to a howling gale, and engineers
building structures of this kind must
have some system of testing the
calculations they make when designing
them. The only way to make such
tests is to attach ropes horizontally to
the structures at various heights, and
to apply forces through the ropes to
represent wind pressures. It is not
easy to do this in the open, because there
natural wind pressures and other factors
complicate matters. The ideal is to find a
completely protected place, where the
engineers carrying out the tests have to
reckon only with the forces they apply
through their ropes.

The need for a testing station for these
tall structures was realised by Stewarts and
Lloyds Ltd., the well-known makers of
steel tubes and other products, and their
first efforts were devoted to finding a
suitable site within easy reach. Members
of the staff who were familiar with
the limestone quarries worked by the
company at Wirksworth soon recalled the one
known as the Monkey Hole, and as soon s it was
examined it was seen that it was ideal, for
except to a limited extent through the
narrow entrance, the wind cannot blow
upon the structures to be tested.

There is another reason why such a
protected site was suitable for testing tall
structures. This is that there is no difficulty
in finding points for anchoring pulleys in
the rock face of the quarry so that ropes
from the test points on the tower itself
could be lead horizontally to them. Tests
could be carried out on open ground only
if two other towers of similar height were
erected to provide the loading points.

After clearing the site the first thing
to be done was to lay down a universal
type of concrete base to which towers of
different varieties could be fixed. Loads
up to 30 tons will be required for some
tests, so the anchorage points at different
levels had to be made very secure. In a
test in which an increasing force was
applied to the type of anchor selected,
the eye of the anchor broke when a direct
pull of 94 tons was exerted on it, but the
anchor itself gave no sign of having been
disturbed in its rock setting. This clearly
left a good margin of safety.

The loading at each point was obtained
by a pull of 5 tons, which was multiplied
by the usual arrangements of multi-sheave
blocks, a required, up to the
maximum 30 tons. Special winches had
to be designed to apply the loads. These
are equipped with gears designed to keep
the speed of movement of the rope very
low, the rate being about 1 ft 3 in. a
minute, so that the loads are applied
slowly in the tests. There are 12 winches,
one for each of the ropes to the test tower
passing over the pulleys to the loading points,
which number 12. Each has a 2 h.p.
motor, running at 960 r.p.m., but the
main drum makes only half a revolution
a minute because of the special gearing.

The building in which the winches are
installed is opposite the entrance to the
quarry, and a general view of them is given
in the lower illustration on this page.
There are dials to indicate the loads applied
at each of the 12 selected points. Others
show how much the structure under test
has moved at various points. This
deflection measurement is carried out on
wires attached to the structure that pass
over pulleys and down into tubes standing
on the quarry floor. Weights in the
tubes keep the wires taut and a slot in
the tube allows a rough indication of
the movement to be measures against
a scale at the side. The deflection is
measured more accurately by electrical
means, which are so sensitive that
movement of a twentieth of an inch is detected.

The main operator has a microphone
through which he can give directions and
an emergency "Stop Everything" button,
which cuts off power to the winches. Two
other operators control the winches by
means of buttons, which must be held
down all the time the winch is operating.